add support for parsing X509 certs from DER

tonic/src/transport/tls.rs

@@ -1,3 +1,5 @@
+use base64::Engine as _;
+
 /// Represents a X509 certificate.
 #[derive(Debug, Clone)]
 pub struct Certificate {
@@ -20,6 +22,17 @@ impl Certificate {
         Self { pem }
     }
 
+    /// Parse a DER encoded X509 Certificate.
+    ///
+    /// The provided DER should include exactly one DER encoded certificate.
+    pub fn from_der(der: impl AsRef<[u8]>) -> Self {
+        let der = der.as_ref();
+        let pem = der2pem(der);
+        Self {
+            pem: pem.into_bytes(),
+        }
+    }
+
     /// Get a immutable reference to underlying certificate
     pub fn get_ref(&self) -> &[u8] {
         self.pem.as_slice()
@@ -57,4 +70,20 @@ impl Identity {
         let key = key.as_ref().into();
         Self { cert, key }
     }
+
+    /// Parse a DER encoded certificate and private key.
+    ///
+    /// The provided cert must contain exactly one DER encoded certificate.
+    pub fn from_der(cert: impl AsRef<[u8]>, key: impl AsRef<[u8]>) -> Self {
+        let cert = Certificate::from_der(cert);
+        let key = key.as_ref().into();
+        Self { cert, key }
+    }
+}
+
+fn der2pem(der: &[u8]) -> String {
+    const RFC7468_HEADER: &str = "-----BEGIN CERTIFICATE-----";
+    const RFC7468_FOOTER: &str = "-----END CERTIFICATE-----";
+    let pem = crate::util::base64::STANDARD_NO_PAD.encode(der);
+    format!("{RFC7468_HEADER}\n{pem}\n{RFC7468_FOOTER}\n")
 }